This application is based on patent application Ser. No. 10-302806 filed on Oct. 23, 1998 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a printing apparatus and a method for correcting print positions and more specifically to a method for registering print positions when a plurality of print heads print in both forward and backward scans.
2. Description of the Prior Art
An ink jet printing method, because of its advantages such as a low noise, a low running cost and ease with which to reduce an apparatus size and produce color images, has found a wide range of applications as in printers and copying machines. Such an ink jet printing method ejects ink droplets from nozzles to form ink dots on printing paper thereby producing an image. In producing a color image, a plurality of print heads are used and the printing is often performed in both directions of scan (hereinafter also referred to simply as a xe2x80x9cbidirectional printingxe2x80x9d) to enhance a printing speed.
In the bidirectional printing using the plurality of print heads, registration of print positions is relatively important for improving an image quality. In this case, the print position registration is performed for following positional deviations with respect to the scan direction of the print heads. It should be noted that there are two types of bidirectional printing: one performs a plurality of scans over the same area to complete an image and the other performs a single scan over any particular area to complete the printing and feeds paper between the forward scan and the backward scan. This specification assumes mainly the former type of the xe2x80x9cbidirectional printingxe2x80x9d in the following descriptions but also includes the latter type. In the latter case, the print position deviation becomes critical at a boundary between scanned areas.
1) Print position deviation between forward and backward printing.
2) Print position deviation among a plurality of print heads arranged in a scan direction.
In an apparatus other than the above-mentioned serial type printing apparatus, such as a full line type printing apparatus in which the printing paper is fed with respect to the print heads, the print position registration is performed to eliminate print position deviations among the print heads in the paper feed direction.
A reason for which the print position registration stated above is required is as follows. As for the positional deviation between the forward and backward printing, it is caused by mechanical factors such as backlash. As for the positional deviation among the print heads, particularly when a plurality of replaceable print heads are used, it is caused by variations of tolerance between the print-heads and the carriage holding them.
In the case of the print position registration between the forward and backward scans in the bidirectional printing for example, a practice to deal with the problems described above involves adjusting a print timing during respective forward and backward scans to change relative print position conditions for the forward and backward scans in a plurality of stages and performing forward and backward scans under these adjusted conditions to print on the printing medium an adjustment pattern consisting of a plurality of lines or the like. On the other hand, in the case of the position registration among the plurality of print heads, it is a practice to change the relative print position conditions of each head as the carriage is scanned in a particular direction and similarly print an adjustment pattern consisting of a plurality of lines with each head. The user visually checks these printed patterns, selects the print position condition under which the positions of the printed lines are best aligned, and sets data on the print position condition in a printing apparatus or host computer, thereby correcting the print positions.
The print position correction based on the conventional method described above, however, may pose the following problem when the bidirectional printing is done using a plurality of print heads.
Print positions may deviate due to varying factors, including variations in an ejection angle and a speed of ink droplets ejected from the print head, variations in parallelism between the printing medium and the print head or the carriage holding the print head, and variations in a distance between the print head and the printing medium (also referred to as xe2x80x9cpaper gapxe2x80x9d). To deal with this problem, a conventional method corrects the printing positions as described above and strictly controls manufacturing errors of print heads and a precision of the carriage drive mechanism to minimize the occurrence of the print position deviations per se. This, however, has led to an increase in the cost of the printer and consumables.
The reason that the conventional print position correction method requires an increased precision as described above, in the case of bidirectional printing using a plurality of print heads, will be explained by referring to FIGS. 1A to 1D.
In FIGS. 1A to 1D, a reference numeral 200 denotes a carriage, 201 and 202 print heads, 203 a printing medium such as paper, and 2101-2104 ink dots respectively formed on the printing medium with an ink droplet ejected from the print heads.
FIGS. 1A and 1B represent a relation between the print heads and the printed dots in the case that printing is performed while scanning the print head from left to right in the figure (the scan direction in this case will be taken as a xe2x80x9cforward directionxe2x80x9d). FIGS. 1C and 1D represent the head-and-dot relation in the case that printing is performed while scanning the print head from right to left (the scan direction in this case will be taken as a xe2x80x9cbackward directionxe2x80x9d). Reference signs in the figure are as follows.
X: a physical distance between the nozzle sections of the heads 201 and 202
VCR: a moving speed of the carriage
h: a nozzle-to-paper distance or the paper gap
V1: a speed of the ink droplet ejected from the head 201
V2: a speed of the ink droplet ejected from the head 202
xcex81: an ejection angle of the ink droplet ejected from the head 201 with respect to a direction normal to a plane of the paper
xcex82: an ejection angle of the ink droplet ejected from the head 202 with respect to the direction normal to the plane of paper
Here, the ejected ink droplet speeds V1, V2 and angles xcex81, xcex82 are those when the carriage is at rest. Actual ejection speeds and angles are obtained by combining respective components of the carriage moving speed Vcr with the respective speeds V1, V2 and angles xcex81, xcex82. For the sake of simplicity, such representations are omitted in the figure.
In FIG. 1A, the ink droplet ejected when the head 201 reaches a position above the position A on the printing medium during the forward scan forms a dot 2101. Similarly, in FIG. 1B, the ink droplet ejected when the head 202 reaches the position A during the forward scan forms a dot 2102. These dots land on the paper, deviated by xcex94Xf in the case that the ejection speeds V1, V2 and ejection angles xcex81, xcex82, characteristics of the heads, vary among the heads.
Similarly, in FIG. 1C, the ink droplet ejected when the head 202 is at the position A during the backward scan forms a dot 2103. Similarly, in FIG. 1D, the ink droplet ejected when the head 201 is at the position A during the backward scan form a dot 2104. In this case, also, these dots land deviated by xcex94Xb in the case that the head characteristics differ between the heads.
Amounts of xcex94Xf and xcex94Xb are affected not only by the print head characteristics V1, V2, xcex81, xcex82 but also by the paper gap h and the carriage speed VCR. The parallelism between the carriage and the printing medium, also, is in effect reflected on xcex81, xcex82, influencing the xcex94Xf and xcex94Xb. Because of these influencing factors, the values of xcex94Xf and xcex94Xb differ in most cases and a fixed relationship between these values do not necessarily hold.
As to the print position deviation between the forward and backward printing, the conventional method to deal with such a deviation involves detecting, based on the adjustment pattern described above, a deviation between the dot 2101 formed during the forward scan of one of the two heads, for example a head 201, and the dot 2104 formed during the backward scan of the head, then, correcting the detected deviation or, alternatively, correcting this deviation plus deviations of the head from a predetermined reference position during the forward and backward scans (or a deviation from an ideal value considering these two kinds of deviations). On the other hand, as for the print position deviation between the print heads, the conventional method limits the direction of printing to, for example, only the forward direction, similarly detects the deviation xcex94Xf between the dot 2101 formed by the head 201 and the dot 2102 formed by the head 202, and then corrects this deviation. In this case, a deviation between the dot 2103 and the dot 2104 formed by the two heads during the backward scan, xcex94Xb, is corrected either by the same amount that was used to correct the above xcex94Xf or by a value estimated from the xcex94Xf. Hence, if the print position deviation between the two print heads during the forward scan, xcex94Xf, and the print position deviation during the backward scan, xcex94Xb, differ due to various factors described above, the correction for aligning the print positions cannot be performed appropriately, leaving the print positions deviated during the succeeding printing operations.
FIG. 2 is a schematic diagram showing an example of vertical lines printed after the above-described conventional print position correction was made. As described above, only the line corresponding to the dot 2103 formed during the backward printing is printed deviated by (xcex94Xfxe2x88x92xcex94Xb) from the line corresponding to the dot 2104. To prevent this deviation, the conventional method is required to minimize the aforementioned various factors associated with the deviation, which in turn leads to cost increases of the apparatus. Further, when the number of print heads increases, the control of the heads becomes more important.
An object of the present invention is to provide a printing apparatus and a print position correction method capable of minimizing print position deviations, which occur during bidirectional printing using a plurality of print heads, without having to maintain the precision of the printing apparatus at so high a level.
In a first aspect of the present invention, there is provided a printing apparatus which uses a plurality of print heads and reciprocally scans the plurality of print heads at least at one kind of speed mode to perform printing, and for which correcting print positions of the plurality of print heads is performed, the apparatus comprising:
adjustment pattern printing means for printing at least (2NMxe2x88x921) kinds of print position deviation adjustment patterns, which are printed with a different combination of the print head or a scan direction of the print head or a scan speed of the print head, the respective different combination being used for printing, where M (xe2x89xa71) is a number of scan speeds of the print head subjected to correcting the print positions and N (xe2x89xa72) is a number of print heads;
calculating means for calculating a correction value for the print positions of the plurality of print heads based on inputs according to the at least (2NMxe2x88x921) kinds of print position deviation adjustment patterns printed by the adjustment pattern printing means; and
correcting means for correcting the print positions of the plurality of print heads based on the correction value calculated by the calculating means.
In a second aspect of the present invention, there is provided a printing apparatus which uses a plurality of print heads and scans the plurality of print heads at a plurality of kinds of speed mode to perform printing, and for which correcting print positions of the plurality of print heads is performed, the apparatus comprising:
first adjustment pattern printing means for printing at least (Nxe2x88x921) kinds of print position deviation adjustment patterns at one of a plurality of kinds of scan speeds subjected to correcting the print positions, where N (xe2x89xa72) is a number of a plurality of print heads;
second adjustment pattern printing means for printing at least (Nxe2x88x921) kinds of print position deviation adjustment patterns at the other of the plurality of kinds of scan speeds after the print positions of the plurality of print heads have been corrected based on inputs according to the at least (Nxe2x88x921) kinds of print position deviation adjustment patters printed by the first adjustment pattern printing means;
calculating means for calculating a correction value for the print positions of the plurality of print heads based on inputs according to the at least (Nxe2x88x921) kinds of print position deviation adjustment patterns printed by the second adjustment pattern printing means; and
correcting means for correcting the print position of the plurality of heads based on the correction value calculated by the calculating means.
In a third aspect of the present invention, there is provided a print position correcting method for a printing apparatus which uses a plurality of print heads and reciprocally scans the plurality of print heads at least at one kind of speed mode to perform printing, and for which correcting print positions of the plurality of print heads is performed, the method comprising the steps of:
printing at least (2NMxe2x88x921) kinds of print position deviation adjustment patterns, which are printed with a different combination of the print head or a scan direction of the print head or a scan speed of the print head, the respective different combination being used for printing, where M (xe2x89xa71) is a number of scan speeds of the print head-subjected to correcting the print positions and N (xe2x89xa72) is a number of print heads;
calculating a correction value for the print positions of the plurality of print heads based on inputs according to the at least (2NMxe2x88x921) kinds of print position deviation adjustment patterns printed in the adjustment pattern printing step; and
correcting the print positions of the plurality of print heads based on the correction value calculated in the calculating step.
In a fourth aspect of the present invention, there is provided a print position correcting method for a printing apparatus which uses a plurality of print heads and scans the plurality of print heads at a plurality of kinds of speed mode to perform printing, and for which correcting print positions of the plurality of print heads is performed, the method comprising the steps of:
printing at least (Nxe2x88x921) kinds of first print position deviation adjustment patterns at one of a plurality of kinds of scan speeds subjected to correcting the print positions, where N (xe2x89xa72) is a number of a plurality of print heads;
printing at least (Nxe2x88x921) kinds of second print position deviation adjustment patterns at the other of the plurality of kinds of scan speeds after the print positions of the plurality of print heads have been corrected based on inputs according to the at least (Nxe2x88x921) kinds of first print position deviation adjustment patters printed in the step for printing first adjustment pattern;
calculating a correction value for the print positions of the plurality of print heads based on inputs according to the at least (Nxe2x88x921) kinds of second print position deviation adjustment patterns printed in the step for printing second adjustment pattern; and
correcting the print position of the plurality of heads based on the correction value calculated in the calculating step.
In a fifth aspect of the present invention, there is provided a computer program element of a print position correcting processing for a printing apparatus which uses a plurality of print heads and reciprocally scans the plurality of print heads at least at one kind of speed mode to perform printing, and for which correcting print positions of the plurality of print heads is performed, the program element comprising:
computer program code means to make the computer execute
to print at least (2NMxe2x88x921) kinds of print position deviation adjustment patterns, which are printed with a different combination of the print head or a scan direction of the print head or a scan speed of the print head, the respective different combination being used for printing, where M (xe2x89xa71) is a number of scan speeds of the print head subjected to correcting the print positions and N (xe2x89xa72) is a number of print heads;
to calculate a correction value for the print positions of the plurality of print heads based on inputs according to the at least (2NMxe2x88x921) kinds of print position deviation adjustment patterns printed in the adjustment pattern printing process; and
to correct the print positions of the plurality of print heads based on the correction value calculated in the calculating process.
In a sixth aspect of the present invention, there is provided a computer program element of a print position correcting processing for a printing apparatus which uses a plurality of print heads and scans the plurality of print heads at a plurality of kinds of speed mode to perform printing, and for which correcting print positions of the plurality of print heads is performed, the program element comprising:
computer program code means to make the computer execute
to print at least (Nxe2x88x921) kinds of first print position deviation adjustment patterns at one of a plurality of kinds of scan speeds subjected to correcting the print positions, where N (xe2x89xa72) is a number of a plurality of print heads;
to print at least (Nxe2x88x921) kinds of second print position deviation adjustment patterns at the other of the plurality of kinds of scan speeds after the print positions of the plurality of print heads have been corrected based on inputs according to the at least (Nxe2x88x921) kinds of first print position deviation adjustment patters printed in the process for printing first adjustment pattern;
to calculate a correction value for the print positions of the plurality of print heads based on inputs according to the at least (Nxe2x88x921) kinds of second print position deviation adjustment patterns printed in the process for printing second adjustment pattern; and
to correct the print position of the plurality of heads based on the correction value calculated in the calculating process.
With the above configuration, at least (2NMxe2x88x921) kinds of print position deviation adjustment patterns, each with a different combination of print head, scan direction or a scan speed, are printed. These adjustment patterns can be used, for example, as the adjustment patterns for the print position deviation between a plurality of print heads in each of the forward and backward scan directions. Based on these patterns, it is possible to correct the position deviation between a plurality of print heads in each scan direction. These patterns can also be used as the adjustment patterns for print position deviation of one of the print heads between the forward scan and the backward scan. Based on the latter patterns, it is possible to correct the position deviation of one print head between the forward scan and backward scan. These patterns allow adjustment of the print position deviation between a plurality of print heads and also of the print position deviation for each print head between the forward scan and the backward scan.
The above and the other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.